Preheat the oven to 350°F (175°C). Apply a light layer of nonstick cooking spray to a 9 × 5-inch loaf pan. Line the pan with parchment paper, allowing the paper to extend beyond the two longer sides so the baked loaf can be lifted out easily.
In a medium mixing bowl, thoroughly whisk the flour, cinnamon, salt, baking powder, nutmeg, baking soda, ginger, and allspice. Continue whisking until the spices and leavening ingredients are evenly dispersed throughout the flour.
In a separate large bowl, whisk the room-temperature eggs with the vanilla extract. Add the pumpkin purée and the desired amount of granulated sugar, then mix until the ingredients form a smooth, uniform mixture.
While whisking continuously, slowly stream the olive oil into the pumpkin mixture. Continue mixing until the oil is completely incorporated and the batter appears glossy and well blended.
Add the dry mixture to the wet ingredients. Fold or stir only until no visible streaks of dry flour remain. A few small lumps are acceptable; excessive mixing may produce a dense or firm loaf.
Transfer the batter to the prepared loaf pan and smooth the surface. Scatter the dark brown sugar and pumpkin seeds evenly over the top. Add a few extra pumpkin seeds for garnish, if using.
Bake for 60 to 70 minutes, or until a toothpick inserted into the center of the loaf emerges clean or with only a few moist crumbs attached.
Allow the pumpkin bread to rest in the pan for 15 minutes. Using the parchment-paper overhang, carefully lift the loaf from the pan and place it on a wire cooling rack. Let it cool completely before cutting into slices and serving.